Viral Infections: Causes, Symptoms, and How To Treat Them

What is a viral infection?

Viral infections are behind many common illnesses, such as the common cold. Unlike bacterial infections, viral infections don’t respond to antibiotics. Fortunately, most viral infections resolve on their own within days or weeks. Respiratory tract infections (RTIs), which affect the nose, throat, sinuses, airways, and lungs, are some of the most frequent types of viral infections. Whether it shows up as a viral throat infection, a viral chest infection, or a viral ear infection, most clear up on their own without needing specific treatment.

A viral infection occurs when a virus—a microscopic organism—enters the body, invades healthy cells, and uses them to reproduce. This process can disrupt the normal function of your cells and trigger symptoms of illness.

If you have a strong immune system, your body can usually fight off a viral infection. Often, your immune system will “remember” the virus, granting you immunity to it in the future. However, some viruses remain in your body long-term, causing periodic flare-ups of symptoms over time.

Antibiotics are ineffective against viruses. Most viruses do not need treatment but there are certain antiviral medications which are used for specific conditions e.g. shingles. 

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What are common viral infections?

Many viral infections affect the respiratory tract, causing symptoms in the nose, throat, sinuses, airways, and lungs. Common respiratory tract infections caused by viruses include:

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What are the symptoms of a viral infection?

Viral infections produce a range of symptoms, depending on the virus and the part of the body it affects. Common viral infection symptoms include fever, fatigue, and aches, and some viruses — like measles — can even cause a viral infection rash. You might also ask: is a viral infection contagious? Most are, especially in the first few days of symptoms.

 

Respiratory tract infections

  • The common cold causes a blocked or runny nose, sneezing, coughing, sore throat, headaches, and sometimes a mild fever.
  • The flu causes more intense symptoms, such as a high fever, body aches, fatigue, and difficulty sleeping. Some people may also experience nausea, vomiting, or diarrhoea.

Conditions triggered by a virus

Condition 

Symptoms 

Bronchitis 

Inflammation of the airways causing a persistent cough (sometimes with yellow or green phlegm). 

Laryngitis 

Inflammation of the voice box leading to hoarseness, a sore throat, and coughing. 

Tonsillitis 

Inflammation of the tonsils causing pain when swallowing, a sore throat, and sometimes white spots in the throat. 

Sinusitis 

Inflammation of the sinuses causing facial pain, a blocked nose, and tenderness around the cheeks or forehead. 

Glandular fever 

A fever, severe sore throat, extreme fatigue, and swollen glands. 

Mumps 

Fever, aches, nausea, and painful swollen glands, which may change the shape of the face. 

Measles 

Early symptoms mimic a cold, followed by a distinctive rash. 

Managing viral infections & when to seek help

Viral infections typically don’t require prescription medication unless symptoms are severe or complications arise. If you’re looking into treatment for viral infection or want to know how to treat viral infection, simple self-care is usually enough. To manage mild symptoms at home, you can:

  • Take over-the-counter painkillers, such as ibuprofen or paracetamol.
  • Use cough syrups or throat lozenges to relieve sore throats or coughing.
  • Stay hydrated and rest.

Seek medical advice if:

  • Your symptoms persist for more than two weeks

  • Your symptoms worsen or are very severe

  • You suspect pneumonia

  • Your symptoms persist for more than two weeks

  • Your symptoms worsen or are very severe

  • You have a fever for more than 3 days

  • You have a weakened immune system, are pregnant, are aged over 65 or have a long term health condition

  • You have coughed up blood or have seen blood in your mucus

Pneumonia may require antibiotics (if bacterial) or hospital care in severe cases.

How can I avoid viral infections?

Preventing viral infections can be challenging, but taking the following precautions can reduce your risk:

  • Practice good hygiene - 
    Wash your hands regularly and clean communal surfaces frequently.

  • Get the flu jab - This annual vaccine is free for pregnant women, those over 65, and individuals with certain health conditions.

Frequently asked questions

Here are direct answers to some of the most frequently asked questions about viral infections.

A virus is a small particle that contains genetic information. It cannot reproduce on its own and needs to enter a living cell to make copies of itself. As the virus makes more copies, it can damage the cells and trigger your immune system, which can cause your symptoms  Instead, it needs to infect your cells to viral-infect them and hijack their machinery. Once inside, it starts to replicate, and as the virus continues to viral-replicate, more and more replicating copies spread to nearby cells, which is what triggers your symptoms.

When you're exposed to a virus, your immune system will mount a response to fight back, this involves your body developing specific antibodies, so your body can produce a defence that recognises the virus if you encounter it again. There are occasions where a doctor may test for these antibodies in your blood to check if you have been exposed to a virus in the past and have immunity.  

 Most mild viral infections don't need antiviral medication, but some patients may benefit from antiviral medication e.g. oseltamivir which is sometimes used for influenza. Not everyone is responsive to these medicines, but for those who are, they can shorten how long symptoms last.

This page focuses mainly on respiratory viral infection types, but plenty of viruses cause illness elsewhere in the body. Respiratory syncytial virus (RSV) and parainfluenza commonly affect babies and young children, while rhinovirus is the main cause of the common cold, and adenovirus and enterovirus can cause a range of respiratory and other symptoms. Separately, a gastrointestinal viral infection — caused by viruses like rotavirus or norovirus — leads to gastrointestinal symptoms such as vomiting and diarrhoea, rather than the respiratory symptoms covered on this page.

Yes — coronavirus (including SARS-CoV-2, the virus behind COVID-19) is a viral infection, and covid-like symptoms often overlap with other respiratory viruses covered on this page. Most viral infections resolve on their own, but occasionally one can worsen, and in some cases a virus can develop into pneumonia — which is why it’s important to seek medical advice if your symptoms don’t improve or get significantly worse. 

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